A magnetic composite type damping material of the type described above is disclosed in JP-A-Hei 3-47750, in which an adhesive layer is disposed between a magnetic layer and a constraining layer to form a three-layered structure, the damping material having this three-layered structure being directly attracted to a vibration source by magnetic force of the magnetic layer.
Since the magnetic composite type damping material having the structure described above can be attracted to the vibration source by magnetic force, operability of mounting on the vibration source is good. Further, it has a structure in which an adhesive layer having a low elastic modulus is sandwiched between the magnetic layer having a high elastic modulus and the constraining layer. Shear deformation is produced in the adhesive layer by vibration generated by the vibration source. Vibration energy is converted into thermal energy by shear deformation mainly in the adhesive layer and, thus, the vibration is absorbed.
Further, a damping material having a structure, in which a magnetic material is disposed in the constraining layer, can be directly attracted to a vibration source by magnetic force. So its operability of mounting on the vibration source is good.
Further, in this case, slight slips are produced at the interface of the magnetic layer with the vibration source by vibration generated by the vibration source owing to the fact that it is attracted to the vibration source only by magnetic force. Vibration energy is converted into thermal energy by interfacial friction, which makes it exhibit a vibration damping property.
In a sandwich type damping material having a structure in which an adhesive material (e.g. rubber, etc.) having a small elastic modulus is sandwiched between two constraining plates such as metal plates having a great elastic modulus, in which shear deformation is produced in the sandwiched adhesive material by vibration and in this way vibration energy is converted into thermal energy, in order to transmit vibration generated by the vibration source to the adhesive material having a small elastic modulus, the damping material should be stuck firmly to the vibration source.
As a method for firmly sticking the damping material to the vibration source, it can be tentatively conceived to use adhesive force of an adhesive or mechanical fixing means such as screws, etc. Supposing temporarily that the magnetic composite type damping material described previously is stuck by using an adhesive, although vibration absorbing action by interfacial friction described above cannot be expected, since it is possible to have the damping material held on the vibration source by magnetic force until the adhesive is hardened, it is not necessary to use any holding member by thrusting it with pressure, which is very useful for improving facility of execution.
However, in a damping material, closely contacted with a vibration source by magnetic force, in which vibration damping is realized by converting vibration energy into thermal energy by interfacial friction at a close contact interface, as in the magnetic composite type damping material described previously, although vibration damping characteristics thereof have a property that its temperature dependence is small and that a constant performance can be obtained in a wide temperature range, the absolute value of the loss factor, which indicates the vibration damping effect, is smaller than a peak value thereof of a general constraining type damping material described previously.
Although a general constraining type damping material has the peak of the loss factor in the neighborhood of the glass transition temperature of the adhesive elastic material, supposing temporarily that it is used in a relatively narrow temperature range around the peak, since the loss factor of the magnetic composite type damping material described above is smaller than that of the general constraining type damping material, it is disadvantageous.
However, taking it into account that in a constraining type damping material using shear deformation of the close contact interface, in which vibration damping is performed by converting vibration energy into thermal energy, vibration damping property (loss factor) decreases rapidly apart from the neighborhood of the glass transition temperature of the adhesive material, it can be understood that the magnetic composite type damping material described above is more advantageous in that constant performance can be obtained in a wide temperature range, although the absolute value of the loss factor is not so great.